Definition: The Standardized Field Sobriety Test (SFST) is a battery of 3 tests performed during a traffic stop in order to determine if a driver is impaired. The 3 tests that make up the SFST are the horizontal gaze nystagmus (HGN), the walk-and-turn, and the one-leg stand tests. Developed in the 1970s, these tests are scientifically validated, and are admissible as evidence in court in a majority of states.
Executive Summary: According to researchers, officers trained to conduct SFSTs correctly identified alcohol-impaired drivers over 90% of the time using the results of SFSTs (Burns and Anderson 1995; Stuster and Burns 1998). The SFST consists of three tests administered and evaluated during a traffic stop to determine impairment and probable cause for arrest. The HGN test is performed to observe whether the driver’s eyes involuntarily jerk as a stimulus is moved side to side. Both the walk-and-turn and one-leg stand tests are “divided attention” tests that are easily performed by most sober drivers. They require a subject to listen and follow instructions while performing simple physical movements. Impaired persons have difficulty with tasks requiring their attention be divided between simple mental and physical tasks.
More Detail: The National Highway Traffic Safety Administration (NHTSA) defines the three parts of the SFST as follows (see NHTSA Highway Safety Desk Book):
The horizontal gaze nystagmus (HGN) test: Horizontal gaze nystagmus is an involuntary jerking of the eyeball which occurs as the eyes gaze to the side. Under normal circumstances, nystagmus occurs when the eyes are rotated at high peripheral angles. However, when a person is impaired by alcohol, nystagmus is exaggerated and may occur at lesser angles. An alcohol-impaired person will also often have difficulty smoothly tracking a moving object. In the HGN test, the officer observes the eyes of a suspect as the suspect follows a slowly moving object such as a pen or small flashlight, horizontally with his eyes. The examiner looks for three indicators of impairment in each eye: if the eye cannot follow a moving object smoothly, if jerking is distinct and sustained nystagmus when the eye is at maximum deviation, or if the angle of onset of jerking is prior to 45 degrees of center. The subject is likely to have a BAC of 0.08 or greater if, between the two eyes, four or more clues appear. A 1998 validation study found that this test allows proper classification of approximately 88 percent of subjects. HGN may also indicate consumption of seizure medications, phencyclidine, a variety of inhalants, barbiturates, and other depressants.
In the walk-and-turn test, the subject is directed to take nine steps, touching heel-to-toe, along with a straight line. After taking the steps, the suspect must turn on one foot and return in the same manner in the opposite direction. The examiner looks for eight indicators of impairment: if the suspect cannot keep balance while listening to the instructions, begins before the instructions are finished, stops while walking to regain balance, does not touch heel-to-toe, uses arms to balance, steps off the line, takes an incorrect number of steps, or makes an improper turn. A 1998 validation study found that 79 percent of individuals who exhibit two or more indicators in the performance of the test will have a BAC of 0.08 or greater.
In the one-leg stand test, the subject is instructed to stand with one foot approximately six inches off the ground and count aloud by ones beginning with one thousand (one-thousand-one, one thousand-two, etc.) until told to put the foot down. The officer times the subject for 30 seconds. The officer looks for four indicators of impairment including swaying while balancing, using arms to balance, hoping to maintain balance, and putting the foot down. A 1998 validation study found that 83 percent of individuals who exhibit two or more such indicators in the performance of the test will have a BAC of 0.10 or greater.
There are many factors that might render a person unable to successfully complete one or more of the SFSTs. For instance, regarding the HGN test, the person asked to consent to such a test might be suffering from an eye disease or condition that affects his/her ability to see and consequently confound the test and results. Age, injury or disease could also affect the ability of a person to perform the one-leg stand test or the walk and turn test. As a general rule, an officer should ask the DUI suspect whether they can give any reason why they cannot perform the test and their answer should be carefully noted in the officer’s report. Other disabilities, such as deafness, should be taken into consideration and noted as well.
Admissibility of Standardized Field Sobriety Test Results
In 1981 NHTSA promulgated a federal standard for field sobriety testing procedures. States are not required to adhere to this federal standard. Although some states do not employ the exact procedures, others replicate NHTSA procedures as closely as possible. In Ohio v. Homan, 732 N.E.2d 952 (Ohio, 2000), Ohio became the only state where courts ruled that evidence is “inherently unreliable” and inadmissible when gathered from field sobriety tests that deviate from NHTSA standards. However, this “strict compliance” standard has since softened to a “substantial compliance” standard, as confirmed by the Ohio State Supreme Court in Ohio v. Boczar, 863 N.E.2d 155, 160 (Ohio, 2007).
Furthermore, according to NHTSA, courts in several states have reviewed the admissibility of field sobriety tests and have held that deviations from the administration of simple dexterity tests (one-leg stand and walk-and-turn tests) should not result in the suppression of test results. However, admissibility of the HGN test may be treated differently due to its “scientific nature.” For this reason, HGN results are vulnerable to challenge and likely to be excluded by the court if the test was not administered in strict compliance with established protocols. Appellate courts generally require that, before an opinion can be expressed by an officer who administered an HGN test, the officer must be qualified as an expert or skilled witness for the purpose of administering the test as well as expressing an opinion as to the results. For example see Robinson v. State 982 So.2d 1260, 1261 Fla. App. 1 Dist., 2008.